1. Field of the Invention
This invention relates to a method of producing laminated ceramic capacitors.
2. Description of the Prior Art
Conventionally, in mass-producing laminated ceramic capacitors on a factory scale, a plurality of ceramic green sheets 1 as shown in FIG. 22 are prepared. A plurality of electrically conductive films 2 serving as internal electrodes are printed on each ceramic green sheet 1 leaving gaps 3 and 4 in longitudinal and transverse directions. A plurality of such ceramic green sheets 1 are laminated and then cut along longitudinally and transversely extending cutting lines and then fired. After they are fired, external electrodes 5 are applied thereto.
In laminating said ceramic green sheets 1, they are so arranged that the gaps on one ceramic green sheet 1 are disposed in alignment with the electrically conductive films 2 on another ceramic green sheet 1 in the direction of lamination (direction of thickness). When such laminated body is cut along cutting lines passing through the gaps 3 and 4, laminated chips 6 such as shown in FIGS. 23 and 24 are obtained. FIG. 23 is a longitudinal sectional view and FIG. 24 is a cross-sectional view.
As is clear from FIGS. 23 and 24, a plurality of internal electrodes 7 originating with said electrically conductive films 2 are formed inside each laminated chip 6, said internal electrodes 7 being opposed to each other and separated by ceramic layers 8 originating with said ceramic green sheets 1. Some of the internal electrodes 7 are connected to one external electrode 5a and the others to the other external electrode 5b. Therefore, at locations where connection to the external electrodes 5a and 5b is not desired, there are formed end margins 9 originating with the gaps 3, as shown in FIG. 23.
Further, as shown in FIG. 24, opposite sides of the internal electrodes 7 are formed with side margins 10 originating with the gaps 4. These side margins 10 are necessary for allowing the capacitor to withstand a higher voltage applied to the laminated ceramic capacitor from its surroundings and for preventing undesired shorting electrical connection to the external electrodes 5a and 5b.
To give a description by taking as an example the laminated ceramic capacitor described with reference to FIGS. 22-24, factors which determine the electrostatic capacity obtained by said capacitor include the area of overlapping regions of the internal electrodes 7. That is, the larger the area, the greater the electrostatic capacity.
However, because of the presence of the aforesaid end margins 9 and side margins 10, the total area of the ceramic layers 8 cannot be made to contribute to obtaining electrostatic capacity. Even if the laminated ceramic capacitor is reduced in size, the width of the end margins 9 and side margins 10 cannot be reduced in proportion thereto, and particularly in a small-sized laminated ceramic capacitor it is seen that the ratio of the width W2 of the internal electrodes 7 to the width W1 of the laminated chip 6, for example, as shown in FIG. 24, is reduced. As a result, the ratio of the effective overlapping area of the internal electrodes 7 to the overall area is extremely reduced, thus lowering the space efficiency of this process for obtaining a desired electrostatic capacity.
In addition, as described above, one of the reasons why the end margins 9 or side margins 10 cannot be reduced so much in the case of a small-sized laminated ceramic capacitor is as follows. Usually, the laminated chip 6 as shown in FIGS. 23 and 24 is obtained by preparing large ceramic green sheets 1 each having printed thereon electrically conductive films 2 in longitudinal and transverse rows serving as internal electrodes 7, as shown in FIG. 24, stacking said ceramic green sheets one upon another, and cutting the stack. Thus, when such steps are taken into account, it is necessary to take into account errors in the step of printing the electrically conductive films 2, the stacking step, and the cutting step. Thus, if the end margins 9 or side margins 10 are set with almost no tolerance for error and if said errors are accumulated, it is possible that the desired margins cannot be guaranteed to exist. For example, if the side margins 10 are smaller than a predetermined value, the internal electrodes 7 might sometimes be exposed to the lateral exterior surface of the laminated chip 6, as shown in FIG. 25, which is not desirable.
Thus, so long as the existing production method is employed, the end margins 9 and side margins 10 must be formed with as much allowance for errors as possible. For this reason, it has been impossible to avoid the aforesaid problem of reduced space efficiency of this process for obtaining a desired electrostatic capacity.
Further, due to a shift or variation in the printing of the electrically conductive films 2 or in the stacking of the ceramic green sheets 1 in FIG. 22, alignment of the internal electrodes 7 in the laminating direction would be degraded, as shown in FIG. 26, leading to a decrease in the overlapping area of the internal electrodes 7. This is also a cause of lowering the space efficiency with respect to the volume of the laminated chip 6 and results in producing a variation in electrostatic capacity among the products of laminated ceramic capacitors obtained.